1. Field of the Invention
The present invention relates to hyperbranched polymers useful for a viscosity increasing agent as a biocompatible hydrogel or for a medical material such as an artificial coating agent. The invention also relates to a process for preparing hyperbranched polymers from anhydrosugar-related compounds.
2. Description of the Related Art
A known method for obtaining a hyperbranched carbohydrate polymer includes, for example, the polymerization by the cationic ring cleavage of 1,6-anhydro-β-D-glucopyranose (e.g., Schuerch et al.: J. Am. Chem. Soc., vol. 81, p. 4054, 1959).
This method, however, suffers from the difficulty in controlling a degree of branching and a molecular weight. The resulting hyperbranched carbohydrate polymer is restricted to a sugar having a glucoside linkage composed of a naturally occurring pyranosyl ring. Further, it is difficult to make up a versatile design of hyperbranched carbohydrate polymers including other sugars consisting of furanosyl ring for example or other sugars having no glucoside linkage.
Recently, the synthesis of hyperbranched polyaminosugars by the glycosylation reaction of sugar oxazoline derivatives are reported (Kadokawa, et al.: Angew. Chem. Int. Ed., vol. 37, pp. 2373-2376, 1998; Polym. Adv. Technol., vol. 11, p. 122, 2000). This process is solely applicable to aminosugars and it has the difficulty of the application to other sugars.